Ever wanted to create luminescent designs or safety arrows in your floor, but weren't too crazy about those crappy, glow-in-the-dark stickers? Now a company in the Netherlands called Hidden Safety is marketing luminescent gravel, which can be mixed into concrete floors to create beautiful patterns or just point people the right direction in the dark. The gravel looks ordinary in light, but it is actually absorbing photons (hence, the material is often called photoluminescent). When darkness falls, photons zoom out of the gravel and create a glow.

You can use different colors to create the glow, with many different patterns.

Some prefer to use them as emergency arrows for people in industrial settings or on cruise ships.